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Outline

Designing Effective Urban Stream Buffers

In This Presentation… Why are urban stream buffers important? Benefits of stream buffers Performance criteria for stream buffers Buffer planning considerations Urban stream buffer zones Buffer conflicts and opportunities Buffer design and management Customizing buffer criteria for unique goals and constraints

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Why Are Urban Stream Buffers Important? Documented decline in riparian cover with increased impervious surface in a watershed Documented decline in index of biotic integrity scores with increased impervious surface Provide habitat and runoff filtering

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36 Local Governments Buffer Survey Results (Heraty, 1993) 90% of buffers in private ownership 90% had a neutral or positive impact on property values 26% indicated buffers often impaired during construction Buffer Programs... 30% had significant complaints 25% recently strengthened 48% had “weak” or no notification methods 50% required delineation of buffers on grading/ E&S plans 67% did not record buffers on any official map 60% of property owners unaware of boundaries/ uses Few make forests the vegetative target (predevelopment cover or no target at all)

Benefits of Stream Buffers Allows streams to move laterally over time Prerequisite for future stream restoration projects Reduces watershed imperviousness Reduces small drainage complaints Most effective flood control insurance Allows for forest conservation/reforestation sites Serves as foundation for greenway system Discourages storm drain enclosures Provides sites for stormwater detention ponds Minimizes creation of new fish barriers

Additional Benefits of Urban Aquatic Buffers Provides a separation distance from impervious cover Provides additional streambank erosion protection Can help increase property values Provides food and riparian habitat for wildlife Provides fish and wildlife migration corridors Helps mitigate stream warming Helps promote associated wetland protection Increases pollutant removal? Helps prevent steep slope disturbance

Stormwater Kills!! Flash floods kill about 40 people per year About 45% of deaths involve cars Flash floods cause about a billion dollars of property damage per year 40% of the flood damage is reported to be outside of the mapped floodplain Source: FEMA, NOAA

Basic Performance Criteria for Urban Buffers A setback is not a buffer The floodplain is the core of the buffer Management is as important as width Model Ordinances are available on the internet: www.cwp.org www.stormwatercenter.net More detail on buffer programs and strategies is available in The Practice of Watershed Protection available at www.cwp.org See articles 39 to 44

Buffers and Stream Cooling Urban stream warming from 5 to 15 degrees is caused by a variety of factors: Impervious surfaces Stormwater ponds Stream channel hardening Loss of riparian cover An 80% riparian forest cover provides cooling A 60% riparian forest cover prevents warming

Urban Stream Buffers: Planning Considerations Runoff volumes can greatly increase from predevelopment conditions Stream channel and floodplain geometry may be out of equilibrium Even 2-year stormwater management can exacerbate streambank erosion Runoff is delivered to a stream in one of four ways: Open channels Stormdrain pipes Swales BMP outfalls

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Urban Stream Buffers: Planning Considerations (cont.) Stream buffers DO NOT typically remove pollutants in urban stormwater Buffers are poorly integrated with stormwater BMPs Stream corridors experience heavy use and encroachment Stream buffers remain as private property Many property owners are unaware of buffers existence Buffers are not well protected during construction

Pollutant Removal in Urban Stream Buffers Little reliable monitoring data exists Removal rates for agricultural systems are not transferable Concentrated stormwater flows often bypass buffer Need to “engineer” outer buffer boundary Septic system setback requirements are important

Designing Effective Urban Stream Buffers Stream buffers are more than a line on a map 1st and 2nd order streams comprise 75% of total stream and river mileage Effective stream protection requires strong local ordinances 10 performance criteria exist for local ordinances

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Ten Performance Criteria for Local Ordinances Stream buffer width Three zone urban stream buffers Predevelopment vegetative target for stream buffers Stream buffer expansion and contraction Stream buffer delineation Stream buffer crossings Use of buffers for stormwater treatment and siting BMPs Stream buffer plan review considerations Post-development management of the stream buffer Protecting property rights within stream buffers

Stream Buffer Width Range: 20 to 200 feet Recommended base width 100 feet Special protection areas 150 feet (trout, septic systems, shorelines) Benefits include pollutant removal, flood insurance, wildlife habitat, shading, streambank protection, fish passage, access, and higher property values

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Three-Zone Urban Stream Buffers Each zone has different function, width, vegetative target, and management: Streamside zone: 25 feet of undisturbed forest cover Middle zone: 50 feet or more of managed forest Outer zone: 25 feet of grass or forest setback from structures

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Predevelopment Vegetative Target Many buffer benefits are amplified by forest cover Target is mature predevelopment riparian plant community Determined from undisturbed “reference” floodplain plant communities Turfgrass allowed in outer zone May require succession or reforestation in streamside/middle zones

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Stream Buffer Expansion and Contraction Base width may be expanded to include: Ultimate 100 year floodplain Any steep slopes greater than 25% Four feet per 1% increase in slope over 5% Delineated wetlands, critical habitats, forest conservation 25 feet more for 3rd and 4th order streams 50 feet for fifth order rivers

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Stream Buffer Delineation Start with USGS 7.5 minute quad map - all “blueline” streams at a minimum However, these do not reveal all first order streams or their exact origin Field delineation: Distinct channel with unvegetated streambed and high water marks, or Upper limit of running water in wet season Inner edge of buffer may be stream centerline or bank depending on stream order

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Stream Buffer Crossings The number and kind of stream buffer crossings are clearly defined Create an unbroken corridor that supports fish passage Width: minimum right of way needed for access Angle: perpendicular to stream Frequency: no more than one crossing/1000 feet Depth: utilities three feet below streambed Capacity: convey ultimate 100 year storm Culverts: bottomless, slab, arch or box designs preferred

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Buffers for Stormwater Treatment & Siting BMPs The stream buffer is one element of the total stormwater treatment system for the watershed Locating structural BMPs (e.g. large ponds and wetlands) in buffers should be restricted to: No more than 100 acres contributing drainage, or Within the first 500 feet of a perennial stream Off-line location in middle or outer zone Urban stream buffers can provide limited filtering of stormwater: Up to 75 feet of adjacent impervious areas Up to 150 feet of adjacent pervious areas (including rooftops)

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Buffers and Urban Stormwater: Conflicts and Opportunities Pollutant removal frequently cited as justification for urban stream buffers (61% of local governments) Little evidence that buffers actually remove urban pollutants in stormwater Best performance is for systems with level spreader and 150 feet of mowed grass (Yu et. al, 1990) Most sites will require a BMP for long-term pollutant removal Small structural BMPs need to be carefully integrated into buffer system

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Measured Pollutant Removal Capability of Selected Urban Vegetated Filters BMP TSS TP Zinc Lead Grass channels 81 40 71 67 Filter Strip - 75’ 54 -25 47 -16 Filter Strip - 150’ 84 40 55 50 Mean Non-Urban 73 56 NA NA

Stream Buffer Plan Review Considerations Buffer boundaries & uses must be clearly defined: Delineate on preliminary and final plans Verify stream delineation in field Check for expansions, crossings, & stormwater treatment Mark boundaries on all construction plans Preconstruction walk-through Fencing of boundaries

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Post-Development Management of the Stream Buffer Maintain visibility of buffer after development: Mark boundaries Educate landowners about boundaries and benefits Clear notification upon resale Bufferscaping programs Annual buffer walks to check for encroachment

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Protecting Property Rights Within Stream Buffers Intent is to change the location of development within a parcel, not its density.  Local governments may wish to use some of these tools: Maintaining buffers in private ownership Buffer averaging Fair and timely administrative appeals Conservation easements and property tax     reduction Stormwater management volume credits

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Density Compensation

Density Compensation Example: Parcel size: 10 ac Housing density: 2 du/ac Estimated number of homes: 20 % parcel delineated as buffer: 15% Density credit: 1.1 Buildable parcel size = (10 ac) (85%) = 8.5 ac Adjusted housing density = (2 du/ac) (1.1) = 2.2 du/ac Adjusted number of homes = (8.5 ac) (2.2 du/ac) = approximately 19 homes (18.7)

Community and Owner Concerns While 80% of buffer programs report strong public support, there are some resident concerns: Access Illegal uses and policing Obstruct water view Taxed on land they cannot utilize Need for composting/firewood Varmints/weeds/ticks

Buffer Considerations How much of the aquatic corridor can be protected by buffers? How should buffers be managed & crossed? What kinds of water dependent uses can be restricted? Should public access be restricted to designated areas? Is restoration or better stewardship possible along an aquatic corridor that has already been developed? How will the buffer network be managed? Long-term maintenance? How much pollutant removal is to be expected?

Customize Buffer Criteria for Unique Watersheds Buffers must be adapted for local watershed management objectives: Lake shorelines Greenways Impacted/non supporting streams Reservoir protection Arid and semi-arid climates Flat and steep terrains Rural land uses Septic versus sewer

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Aquatic Buffers: Summary Buffers can be implemented various ways to protect riparian stream corridors, lakes and coastal areas. Buffers are typically a low-cost means for meeting some stormwater management goals, improving water quality, and providing habitat. Buffers provide flood hazard mitigation and physical separation distance between humans and waters. Buffers can be adapted to various development, political and physical landscapes.